This application claims priority under 35 U.S.C. xc2xa7119 on European Application No. EP 01119261.4 which has a filing date of Aug. 9, 2001, the entire contents of which are hereby incorporated by reference.
The invention generally relates to a gas turbine, having a number of turbine blades/vanes respectively combined to form blade/vane rows. Preferably, each of the turbine blades/vanes has an integrated cooling air duct. It also generally relates to a method of operating a gas turbine.
Gas turbines are employed in many fields for driving generators or machinery. In this process, the energy content of a fuel is used to generate a rotational motion of a turbine shaft. For this purpose, the fuel is burnt in a combustion chamber, with compressed air being supplied from an air compressor. The working medium at high pressure and at high temperature generated in the combustion chamber by the combustion of the fuel is conducted, in this process, via a turbine unit connected downstream of the combustion chamber, where the gas expands with an output of work.
In order to generate the rotational motion of the turbine shaft in this process, a number of rotor blades, which are usually combined into blade groups or blade rows, are arranged on this turbine shaft and these rotor blades drive the turbine shaft by means of a transfer of inertia from the flow medium. In order to conduct the flow medium within the turbine unit, furthermore, guide vane rows connected to the turbine casing are usually arranged between adjacent rotor blade rows.
In the design of such gas turbines, a usual design objectivexe2x80x94in addition to the achievable powerxe2x80x94is a particularly high efficiency. For thermodynamic reasons, an increase in the efficiency can fundamentally be obtained by increasing the outlet temperature at which the working medium flows out of the combustion chamber and into the turbine unit. In consequence, temperatures of approximately 1200xc2x0 C. to 1300xc2x0 C. are an objective for such gas turbines and are also achieved.
In the case of such high temperatures of the working medium, however, the components and structural parts exposed to this working medium are subjected to high thermal stresses. In order, nevertheless, to ensure a comparatively long life of the components affected whole maintaining a high level of reliability, cooling is usually provided for the components affected, in particular for the rotor blades and/or guide vanes of the turbine unit. The turbine blades/vanes are therefore usually designed so that they can be cooled, it being particularly necessary to ensure an effective and reliable cooling of the first blade/vane rows, viewed in the flow direction of the working medium. For cooling purposes, the respective blade/vane in this arrangement usually has a coolant duct, which is integrated into the blade/vane aerofoil or the blade/vane profile and from which a coolant can be specifically conducted to the thermally stressed zones, in particular, of the turbine blade/vane.
In this arrangement, cooling air is usually employed as the coolant. This cooling air is usually supplied to the respective turbine blade/vane, in the manner of an open cooling system, via an integrated coolant duct. After emerging from the latter, the cooling air flows, in branch ducts, through the respectively provided regions of the turbine blade/vane. At the outlet end, these ducts are left open so that, after flowing through the turbine blade/vane, the cooling air emerges from the latter and, in the process, mixes with the working medium conducted in the turbine unit.
In this way, it is possible to make a reliable cooling system for the turbine blade/vane available with comparatively simple means, it being also possible to admit coolant, in an appropriate manner, to thermally particularly stressed zones of the turbine blade/vane. With respect to the introduction of the cooling air into the working medium conducted in the turbine unit, on the other hand, it is however necessary to pay attention to ensuring that its characteristic parameters, such as pressure and temperature, are consistent with or are compatible with the corresponding parameters of the working medium. In particular, only limited heating of the cooling air is permissible during the cooling of the turbine blades/vanes so that, precisely in the case where comparatively high outlet temperatures are desired for the working medium, a particularly large quantity of cooling air is necessary. This, in turn, has the effect of limiting the efficiency of the gas turbine.
An economy in the cooling air requirements, which is desirable for these reasons, can be achieved by configuring the cooling system as a closed cooling system. In a closed cooling system of this type, the used cooling air is returned to the combustion process. Particularly in the case of such a closed cooling system, however, in which the cooling air can be subject to a comparatively high pressure loss, it is usually necessary to provide cooling air which is matched to the location and requirement and has a comparatively high pressure, which depends on the injection location provided. In this arrangement, the pressure loss in the conduction of the cooling air through a closed system has inter alia also to be taken into account. Precisely in the case of comparatively long, extended systems, the pressure loss can contribute to a substantial extent to the requirements with respect to the cooling air which has to be provided. Precisely the provision of cooling air with comparatively high pressure does, however, involve a comparatively complicated design of the associated systems; particularly in the case of high pressure requirements, the cooling air compressor necessary for providing the cooling air can, depending on the operating conditions, partially or indeed completely counterbalance the efficiency and power advantages attainable due to the closed cooling system.
An embodiment of the invention is therefore based on an object of providing a gas turbine in which, while maintaining reliable cooling of the turbine blades/vanes, the cooling air requirement is kept particularly low. In addition, a particularly suitable method for operating such a gas turbine with a comparatively small cooling air requirement overall is to be provided.
With respect to the gas turbine, an object may be achieved, according to an embodiment of the invention, by the turbine blades/vanes forming a first turbine blade/vane row and the turbine blades/vanes forming a second blade/vane row connected downstream of the first blade/vane row, viewed in the flow direction of the working medium, being connected one behind the other on the cooling air side with the intermediate connection of an injection device for water.
An embodiment of the invention then takes into consideration that the cooling air requirement for reliable cooling of the turbine blades/vanes can be kept particularly small by employing the cooling air to a particularly intensive extent for cooling the turbine blades/vanes. With respect to the necessary operating pressure of the cooling air, this is, in particular, possible in the case of the cooling air which has to be made available at a comparatively high pressure in any case for the turbine blade/vane rows located comparatively far forward, viewed in the flow direction of the working medium. The cooling air for these turbine blade/vane rows has to be made available, for operational reasons, at such a high pressure that this pressure level is sufficient for conducting cooling air over a plurality of turbine blades/vanes or blade/vane rows connected on the cooling air side in sequence, even taking account of comparatively high pressure losses when cooling the blades/vanes.
In order to utilize this pressure potential, provision is made for employing the still available pressure of the cooling air flowing out of the first blade/vane row, which has now been cooled, for feeding the second blade/vane row which still has to be cooled. In this arrangement, however, it is necessary to take account of the fact that the cooling air flowing out of the first blade/vane row has been heated by the cooling of the first blade/vane row. In order, nevertheless, to be able to employ this cooling air to cool the second blade/vane row also, intercooling of the cooling air is provided before its entry into the second blade/vane row. For this purpose, while maintaining the pressure of the cooling air, its temperature is reduced in such a way that a renewed use of the cooling air in the next blade/vane row is made possible. In this arrangement, the intercooling takes place by injecting water, the outlets of the cooling air ducts of the turbine blades/vanes forming the first blade/vane row, viewed in the flow direction of the working medium, being connected, with the intermediate connection of an injection device for water, to the inlets of the cooling air ducts of the turbine blades/vanes forming the blade/ vane row which is next in order, viewed in the flow direction of the working medium.
Advantageously, such multiple utilization of the cooling air is provided for the cooling of guide vanes of the gas turbine. For this purpose, the first and the second blade/vane rows are respectively formed as a guide vane row by a number of guide vanes connected to a turbine casing of the gas turbine. In this arrangement, the cooling air conduction between the guide vane rows expediently takes place by means of a duct system integrated in the turbine casing, the water injection being also arranged in the turbine casing.
In an alternative or additional advantageous further development, such a multiple utilization of the cooling air is, however, also provided for rotor blade rows of the gas turbine. For this purpose, the first and the second blade/vane rows are expediently and respectively formed by a number of rotor blades arranged on a turbine shaft of the gas turbine. In this case, the duct system for conducting the cooling air is expediently integrated in the turbine shaft.
In a particularly advantageous embodiment, such multiple utilization is provided both for the cooling air for the rotor blades of the gas turbine and for the cooling air for the guide vanes of the gas turbine. For this purpose, in a particularly advantageous further development, both the rotor blade rows following one another, viewed in the flow direction of the working medium, and the guide vane rows following one another, viewed in the flow direction of the working medium, are connected one behind the other, on the cooling air side, in each case with the intermediate connection of an associated injection device for water.
Between the blade/vane rows which are connected one behind the other in this manner on the coolant side, the cooling air is essentially conducted in the manner of a closed cooling system. In order to permit, with certainty, reliable cooling of particularly critical regions of individual blades/vanes also, however, provision is advantageously made for releasing some of the cooling air, to suit the requirement, in the manner of an open cooling system in particularly affected regions of individual turbine blades/vanes or of all the turbine blades/vanes. For this purpose, a number of the turbine blades/vanes expediently have a number of cooling air outlets in the region of the rear edge, viewed in the flow direction of the working medium, of their blade/vane aerofoils. With respect also to the pressure level of the cooling air conducted within the turbine blades/vanes, this is readily possible precisely for the turbine blades/vanes arranged comparatively for toward the rear, viewed in the flow direction of the working medium, because the pressure drop in the flow duct of the working medium of the gas turbine can be up to 12 bar and is therefore greater, in the case of turbine blades/vanes which are connected one behind the other on the coolant side, than the pressure loss in the cooling air duct itself.
With respect to an embodiment of the method, an object may be achieved by the cooling air flowing out of the turbine blades/vanes which form the first blade/vane row being intercooled by the injection of water and being subsequently supplied to the cooling air ducts of the turbine blades/vanes forming the second blade/vane row.
Such a concept of cooling designed for an essentially closed cooling system can be advantageously combined with an open cooling system, which is matched to the requirement, for regions of the turbine blades/vanes which are particularly subjected to thermal effects. For this purpose, a partial flow of the cooling air flowing through a turbine blade/vane is expediently branched off within the latter and is mixed into the working medium by a number of cooling air outlets arranged in the region of the rear edge, viewed in the flow direction of the working medium, of its blade/vane aerofoil.
The advantages achieved can include, in particular, the fact that due to the connection, one behind the other on the cooling air side, of a plurality of turbine blades with intercooling of the cooling air by the injection of water, a particularly effective utilization is made possible for the cooling air, which has to be made available at a comparatively high pressure in any case for the blade/vane rows located comparatively far forward, viewed in the flow direction of the working medium. Such a high-pressure and therefore comparatively xe2x80x9chigh-valuexe2x80x9d cooling air can, in this arrangement, be subjected to multiple utilization so that the cooling air consumption is kept particularly small overall. Because of this, provision of separately compressed cooling air is not, in particular, necessary for blade/vane rows located comparatively further to the rear.
Such a multiple use of the cooling air can be provided for only two or also for three or more blade/vane rows following one another, viewed in the flow direction of the working medium. The multiple use of the cooling air, while utilizing the pressure still also available in the cooling air flowing out of the first blade/vane row is, in particular, made possible because a pressure drop of approximately 12 bar exists overall along the flow duct of the working medium within the gas turbine.
Due to the release, to suit the requirement, of a partial quantity of the cooling air in order to feed, in the manner of an open cooling system, comparatively severely thermally affected regions of individual turbine blades/vanes, an essentially per se closed but overall open air cooling system results, in which only the cooling air consumption in the first blade/vane row occurs, whereas the system dispenses with the additional consumption of cooling air in the following blade/vane rows.